Electron discharge device



Patented Dec. 12, 1944 ELECTRON DISCHARGE DEVICE Otto H. Schade, West Caldwell, N. J., assignmto Radio Corporation of America, a corporation of Delaware Application May 30, 1942, Serial No. 445,186

3 Claims.

This invention relates to a power supply circuit, and more particularly to a circuit for providing plate voltage for sawtooth deflection voltage generators for cathode ray tubes.

In some applications of cathode ray tubes, it is desirable to produce a deflection of constant amplitude at a constant repetition rate, but having a variable velocity of sweep and a correspondingly varying period of dwell between successive deflections. A consideration of the power requirements of a sawtooth sweep generator or sweep amplifler'in this type of service shows that a plate supply having high voltage and low current capability is required with a high velocity sweep, and one having relatively low voltage and high current capability is required with a low velocity sweep. For example, assume the deflection repetition time to be fixed at 1000 microseconds. In a magnetic deflection circuit, a constant deflection amplitude requires a constant peak current; assume this to be 200 milliamperes. The average value of a cyclically repeating sawtooth current pulse is one half the peak value multiplied by the ratio of the duration time of the sawtooth to the repetition time. Thus a wave having a peak current of 200 milliamperes requires an average current of 100 milliamperes for a pulse of 1000 microseconds duration, 10

milliamperes for a pulse of 100 microseconds dur-.

ation and 1 milliampere for 10 microseconds duration, with a repetition time of 1000 microseconds.

The saw tooth current develops a voltage drop on the deflection coils given by i E I EB P The last two columns give the required plate supply voltage and power input for a power tube operating at a minimum plate potential of 80 volts. It is evident that in this particular case a power supply of around 600 volts is necessary in order to deflect the beam across the screen in 10 microseconds, repeating at intervals of 1000 microseconds. The average current required is only 1 milliampere. However, an average current of 100 milliamperes is required to deflect the beam in 1000 microseconds, repeating every 1000 microseconds.

A constant voltage power supply capable of meeting the foregoing requirements would deliver watts to the plate of the power tube when the sawtooth duration time is 1000 microseconds, and only 10 watts power is required. The remaining 50 watts would be dissipated in heating the power tube. If, on the other hand, the plate supply voltage is varied inversely as the sawtooth duration time, only one sixth as much power is necessary. There is correspondingly less heating of the power tube, and the power supply can be smaller and consequently lighter and cheaper.

Accordingly it is an object of my invention to provide an improved device for supplying plate voltage for sawtooth wave generators and amplifiers. A further object of the invention is to provide an improved variable voltage power supply suited to the peculiar requirements of a constant amplitude, constant repetition time sawtooth wave generator or amplifier, as described above. Still another object is the provision of an improved power supply unit having automatic regulation such that it supplies a voltage which is a predetermined function of the load. These and other and incidental ob- Jects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawing, in which Figs. 1a, 1b and 1c are graphs of sawtooth waves; Fig. 2 is a schematic block diagram of the device of the invention; and Figs. 3 and 4 are circuit diagrams of two specific embodiments of the invention.

Referring to Figs. 1a, 1b and 1c, the sawtooth waves A, B and C each have a repetition time of 1000 microseconds, and a peak amplitude of 200 milliamperes. The duration of each pulse of the wave A is 1000 microseconds, of wave B, microseconds, and wave C, 10 microseconds. The average current in each case is the area within the sawtooth divided by the ratio of repetition time to sawtooth time. It is apparent from examination of Fig. In. that the slope of the sawtooth varies inversely as its duration. The rate of change of current with respect to time is highest when the sawtooth duration is shortest, producing the largest inductive drop in the deflecting coils through which it is conducted.

Referring to Fig. 2, two power sources I and 3 are connected in series in the plate circuit of the tube 6, which also includes the cathode ray defiection coils L. The source I is adapted to provide a low voltage and high currents, for example, 150 volts and 100 milliamperes, with good regulation, and the source 3 is adapted to provide high voltage and low current, such as 450 volts and 1 milliampere, with relatively poor regulation. A diode I is connected across the source 3 to short circuit it when large currents are required to prevent an output voltage drop below that of the low voltage supply I.

Referring to Fig. 3, a fullwave low voltage rectifier 8, capable of supplying, for example, 150 volts and 100 milliamperes with reasonably good regulation, has its output circuit connected in series with that of a rectifier II. A.-C. voltage is applied to the anodes of the rectifier 9 through a center tapped transformer Ill. The cathode of the rectifier 9 is connected through a filter circuit including a choke I3 and a capacitor 14 to the negative side of the output circuit of the rectifier II. The rectifier ii is energized from the portion of the ripple voltage on a filter choke I3 in the circuit of the rectifier 9, which excites a resonant circuit comprising inductance I5 tuned to the ripple frequency by a capacitor H. A tap IS on the choke I3 is adjusted so that the rectifier I I will provide an output voltage of, for example, 450 volts at a load of 1 milliampere. A diode 2| is connected across the output circuit of the rectifier II. The high impedance tuned circuit I5, IT can only supply small currents. For high current demands, its Voltage falls off and most of the load current flows directly from the low voltage circuit 8 over the diode 2|.

Referring to Fig, 4, a similar circuit is shown including a resistor 23 in serieswith a high voltage rectifier to limit the current obtainable at high voltage. A relatively high A.-C. voltage is applied to the rectifier 25 from a secondary winding 24 of a transformer 26, A center tapped secondary winding 28 is provided on the transformer 25 and connected to the anodes of a full wave rectifier 29. The center tap of the winding 28 is connected to the negative output terminal of the rectifier 29. The output circuit of the rectifier 29 includes a filter choke 33 and a capacitor 35. The positive terminal of the outwhere is the average current for 10 microsecond operation, at which the output voltage of E2 of the rectifier 25 will decrease only 10 percent due to the resistor 23. The current in the resistor 23 is hence limited to 10 Inc) for the 100 and 1000 microsecond operation, resulting in a power loss of only one tenth that obtained .with a single supply of fixed voltage.

I claim as my invention:

1. A power supply system for sawtooth wave generators comprising a low voltage source of electrical energy, a high voltage source connected in series therewith, and a rectifier connected across said high voltage source.

2. A power supply system comprising a rectifier circuit, a filter including an inductor connected in the output circuit of said rectifier, a resonont circuit including a portion of said inductor, a second rectifier circuit having its input terminals connected across one of the reactance elements of said resonant circuit and its output circuit connected in series with the output cir-, cuit of said first rectifier, and a unidirectionally conductive device connected across the output terminals of said second rectifier circuit.

3. A power supply system for sawtooth deflection voltage generators for cathode ray tubes comprising a relatively low voltage source of electrical energy having low internal resistance, a relatively high voltage source of electrical energy having high internal resistance, a utilization circuit, connections whereby said sources are connected in additive series relation to said utilization circuit, and a unidirectionally conductive device connected across said high voltage source so as to prevent reversal of the polarity of the voltage between the output terminals of said high voltage source.

OTTO H. SCHADE. 

